User station for a serial bus system, and method for communicating in a serial bus system

ABSTRACT

A user station for a serial bus system, including a communication control device for controlling a communication of the user station with at least one other user station of the bus system, and a transceiver device for transmitting a transmission signal, generated by the communication control device, onto a bus of the bus system. The communication control device is designed to generate the transmission signal according to a frame, and to insert into the frame at least one field that is designed for checking whether the bit stream of the frame in a user station of the bus system that receives the frame is shifted by at least one bit compared to the expected frame.

FIELD

The present invention relates to a user station for a serial bus system,and a method for communicating in a serial bus system that operates witha high data rate as well as great flexibility and with a high level oferror robustness.

BACKGROUND INFORMATION

Bus systems for the communication between sensors and control units, forexample in vehicles, are intended to allow the transfer of a large datavolume, depending on the number of functions of a technical facility ora vehicle. Often there is a requirement for the data to be transferredfrom the sender to the receiver more quickly than previously, and alsofor large data packets to be transferable as needed.

At the present time, in vehicles, a bus system is used in theintroduction phase, in which data are transferred as messages under theISO 11898-1:2015 standard, as a CAN protocol specification with CAN FD.The messages are transferred between the bus users of the bus system,such as the sensor, control unit, transducer, etc. With mostmanufacturers, CAN FD is used in the vehicle at a 2 Mbit/s data bit rateand a 500 kbit/s arbitration bit rate in the first step.

To allow even higher data rates, at the present time a successor bussystem for CAN FD (referred to below as CAN XL) is being developed. Inaddition to the strict data transport, CAN XL is intended to alsosupport other functions via the CAN bus, such as functional safety, datasecurity, and quality of service (QoS). These are basic properties thatare required in an autonomously traveling vehicle.

Errors may always occur during the transfer of data in a frame via achannel (CAN bus), in particular due to external influences, inparticular irradiation. The task of the communication protocol of CANXL, among other things, is to detect and discard erroneously receivedframes. The quality of the error detection may be expressed by theresidual error probability. The residual error probability indicates howlikely it is that a frame is accepted as correct, despite errors in areceiving user station (reception node) of the bus system that is not asender of the frame.

For the functional safety of a system, it is very advantageous andimportant for the residual error probability to be as small as possible.Class 1 errors, namely, bits (bit flips) sampled erroneously in aninverted manner, and/or class 2 errors, namely, locally accumulated biterrors (burst errors), that are transferred in the frame may be detectedwith the aid of a check sum (cyclic redundancy check (CRC)).

However, it is problematic when edges are generated or shifted due toexternal irradiation. As a result, the receiving user station (receptionnode) of the bus system, which is not a sender of the frame, may carryout shifted sampling of the bit stream in the received frame. Thesampling of the bit stream may be shifted by one or multiple bits, whichis also referred to as class 3 errors. For these types of errors, such areceiving user station is not able to reliably detect the error, usingthe check sum (CRC).

SUMMARY

An object of the present invention is to provide a user station for aserial bus system, and a method for communicating in a serial bussystem, which solve the above-mentioned problems. In particular, onobject of the present invention is to provide a user station for aserial bus system, and a method for communicating in a serial bussystem, in which errors due to additional or shifted edges in a bitstream are detected with high reliability in order to achieve a highlevel of error robustness of the communication, even for a high datarate and an increase in the quantity of the useful data per frame.

The object may be achieved by a user station for a serial bus system inaccordance with the present invention. In accordance with an exampleembodiment of the present invention, the user station includes acommunication control device for controlling a communication of the userstation with at least one other user station of the bus system, and atransceiver device for transmitting a transmission signal, generated bythe communication control device, onto a bus of the bus system, so thatfor a message that is exchanged between user stations of the bus system,the bit time of a signal transmitted onto the bus in the firstcommunication phase may be different from a bit time of a signaltransmitted in the second communication phase, the communication controldevice being designed to generate the transmission signal according to aframe, and to insert into the frame at least one field that is designedto check whether the bit stream of the frame in a user station of thebus system that receives the frame is shifted by at least one bitcompared to the expected frame.

Due to the embodiment of the user station, the residual errorprobability for a frame that is received from the bus may be reduced. Asa result, a receiver of the frame may decode the correct frame length,and therefore also check the check sum (cyclic redundancy check (CRC))at the end of the frame at the correct position. Errors in thecommunication in the bus system may thus be detected quickly andreliably.

By use of the user station, it is possible to guarantee the detection ofa shifted data stream up to an N-bit shift. This allows a reliabletransfer of frames via the bus, even in the event of irradiation.

It is also advantageous that the measures for reducing the residualerror probability, with regard to class 3 errors, additionally requireonly a very small number of control bits. The new field FCP is therebyaccommodated in the frame very innovatively. As a result, the dataoverhead in addition to the useful data actually to be transferred isvery low.

When each fixed stuff bit is replaced by an FCP field, the data overheadmay even be zero. In addition, the format check is very powerful, sincemultiple fixed stuff bits and therefore FCP fields are replaced. Due tothe data overhead, which is low or is not increased, the transferablenet data rate may be optimized, so that the communication in the bussystem is slowed down no more than necessary.

As a result, by use of the user station, transmission and reception ofthe frames may be ensured with great functional safety and greatflexibility with regard to instantaneous events during operation of thebus system and at a low error rate, even with an increased volume ofuseful data per frame.

By use of the user station in the bus system, it is thus possible inparticular to maintain an arbitration from CAN in a first communicationphase and still increase the transfer rate considerably compared to CANor CAN FD.

A method carried out by the user station may also be used when at leastone CAN user station and/or at least one CAN FD user station thattransmit(s) messages according to the CAN protocol and/or CAN FDprotocol are/is present in the bus system.

Advantageous further embodiments of the user station are disclosedherein.

According to one exemplary embodiment of the present invention, thecommunication control device is designed to insert the at least onefield into the frame after a data field. The communication controldevice may be designed to insert the at least one field into the frameafter a frame check sum that has been formed over all bits in the frame.

According to another exemplary embodiment of the present invention, thecommunication control device is designed to insert the at least onefield prior to a data field in which useful data of the frame areinserted.

For a particularly high net data rate, the communication control deviceis designed to configure and/or arrange the at least one field in such away that the contents of the at least one field in a receiving userstation are to be used not only for the function of checking the shiftof the bit stream, but also for a different function.

According to yet another exemplary embodiment of the present invention,the communication control device is designed to always insert one of thestated fields into the frame after a fixed number of bits.

It is possible for the communication control device to be designed toinsert the at least one field into the frame as a fixed stuff bit, thecommunication control device being designed to insert all fixed stuffbits into the frame according to a fixed bit stuffing rule, according towhich a fixed stuff bit is to be inserted after a fixed number of bits.The communication control device is possibly designed to select thevalue of the field as a function of which value would be selected forthe stuff bit in order to insert an inverse stuff bit into the frameafter five identical bits in succession.

The communication control device is optionally designed to use the samevalue for all the above-mentioned fields in the frame.

In one particular embodiment of the present invention, the communicationcontrol device is designed to use an even number of M bits for the atleast one field, the first half of the M bits in each case having thesame first value, and the second half of the M bits in each case havingthe same second value, which is inverse to the first value.

In another particular embodiment of the present invention, thecommunication control device is designed to insert into the at least onefield at least the least significant bits of the number of fixed stuffbits that are inserted into the frame.

In yet another particular embodiment of the present invention, thecommunication control device is designed to insert into the at least onefield at least the least significant bits of the number of frames thathave already been transmitted onto the bus from the communicationcontrol device.

It is possible for the communication control device to be designed toprovide a bit after a switchover of the second communication phase intothe first communication phase, during which the transceiver device hastime to switch over into the second communication phase, thecommunication control device being designed, in the case in which theuser station of the bus system that receives the frame is, however, notthe sender of the frame, to use the bit to check whether the bit streamof the received frame is shifted by at least one bit compared to theexpected frame.

It is possible for the frame that is formed for the message to have adesign that is compatible with CAN FD, in the first communication phaseit being negotiated which of the user stations of the bus system in thesubsequent second communication phase obtains, at least temporarily,exclusive, collision-free access to the bus.

The user station described above may be part of a bus system which alsoincludes a bus and at least two user stations that are connected to oneanother via the bus in such a way that they may communicate seriallywith one another. At least one of the at least two user stations is auser station described above.

Moreover, the object stated above may be achieved by a method forcommunicating in a serial bus system according to an example embodimentof the present invention. The method may be carried out with a userstation of the bus system that includes a communication control deviceand a transceiver device. In an example embodiment of the presentinvention, the method including the steps: controlling, via thecommunication control device, a communication of the user station withat least one other user station of the bus system, and transmitting, viathe transceiver device, a transmission signal, generated by thecommunication control device, onto a bus of the bus system, so that fora message that is exchanged between user stations of the bus system, thebit time of a signal that is transmitted onto the bus in the firstcommunication phase may be different from a bit time of a signal that istransmitted in the second communication phase, the communication controldevice generating the transmission signal according to a frame, andinserting into the frame at least one field that is designed to checkwhether the bit stream of the frame in a user station of the bus systemthat receives the frame is shifted by at least one bit compared to theexpected frame.

The method yields the same advantages as stated above with regard to theuser station.

Further possible implementations of the present invention also includecombinations, even if not explicitly stated, of features or specificembodiments described above or discussed below with regard to theexemplary embodiments. Those skilled in the art will also add individualaspects as enhancements or supplements to the particular basic form ofthe present invention, in view of the disclosure herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below withreference to the figures, and based on exemplary embodiments.

FIG. 1 shows a simplified block diagram of a bus system according to afirst exemplary embodiment of the present invention.

FIG. 2 shows a diagram for illustrating the design of a message that maybe transmitted from a user station of the bus system according to thefirst exemplary embodiment of the present invention.

FIG. 3 shows a simplified schematic block diagram of a user station ofthe bus system according to the first exemplary embodiment of thepresent invention.

FIG. 4 shows a temporal profile of bus signals CAN XL_H and CAN XL_L forthe user station according to the first exemplary embodiment of thepresent invention.

FIG. 5 shows a temporal profile of a differential voltage VDIFF of bussignals CAN XL_H and CAN XL_L for the user station according to thefirst exemplary embodiment of the present invention.

FIG. 6 shows a diagram for illustrating the design of a message that maybe transmitted from a user station of the bus system according to asecond exemplary embodiment of the present invention.

FIG. 7 shows a diagram for illustrating the design of a message that maybe transmitted from a user station of the bus system according to athird exemplary embodiment of the present invention.

Unless stated otherwise, identical or functionally equivalent elementsare provided with the same reference numerals in the figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows as an example a bus system 1 that is in particular thebasis for the design of a CAN bus system, a CAN

FD bus system, a CAN XL bus system, and/or modifications thereof, asdescribed below. Bus system 1 may be used in a vehicle, in particular amotor vehicle, an aircraft, etc., or in a hospital, and so forth.

In FIG. 1, bus system 1 includes a plurality of user stations 10, 20,30, each of which is connected to a first bus wire 41 and a second buswire 42 at a bus 40. Bus wires 41, 42 may also be referred to as CAN_Hand CAN_L or CAN XL_H and CAN XL_L, and are used for electrical signaltransfer after coupling in the dominant levels or generating recessivelevels or other levels for a signal in the transmission state. Messages45, 46 in the form of signals are serially transferable betweenindividual user stations 10, 20, 30 via bus 40. If an error occursduring the communication on bus 40, as illustrated by the serrated darkblock arrow in FIG. 1, an error frame 47 (error flag) may optionally betransmitted. User stations 10, 20, 30 are, for example, control units,sensors, display devices, etc., of a motor vehicle.

As shown in FIG. 1, user station 10 includes a communication controldevice 11, a transceiver device 12, and a format check module 15. Userstation 20 includes a communication control device 21 and a transceiverdevice 22. User station 30 includes a communication control device 31, atransceiver device 32, and a format check module 35. Transceiver devices12, 22, 32 of user stations 10, 20, 30 are each directly connected tobus 40, although this is not illustrated in FIG. 1.

Communication control devices 11, 21, 31 are each used for controlling acommunication of particular user station 10, 20, 30 via bus 40 with atleast one other user station of user stations 10, 20, 30 connected tobus 40.

Communication control devices 11, 31 create and read first messages 45,which are modified CAN messages 45, for example. Modified CAN messages45 are built up based on a CAN XL format, described in greater detailwith reference to FIG. 2, and in which particular format check module15, 35 is used. Communication control devices 11, 31 may also bedesigned to provide a CAN XL message 45 or a CAN FD message 46 fortransceiver device 32 or receive it from same, as needed. Particularformat check modules 15, 35 are also used. Communication control devices11, 31 thus create and read a first message 45 or second message 46,first and second messages 45, 46 differing by their data transmissionstandard, namely, CAN XL or CAN FD in this case.

Communication control device 21 may be designed as a conventional CANcontroller according to ISO 11898-1:2015, i.e., as a CAN FD-tolerantconventional CAN controller or a CAN FD controller. Communicationcontrol device 21 creates and reads second messages 46, for example CANFD messages 46. CAN FD messages 46 may include 0 to 64 data bytes, whichare also transferred at a much faster data rate than with a conventionalCAN message. In particular, communication control device 21 is designedas a conventional CAN FD controller.

Transceiver device 22 may be designed as a conventional CAN transceiveraccording to ISO 11898-1:2015 or as a CAN FD transceiver. Transceiverdevices 12, 32 may be designed to provide messages 45 according to theCAN XL format or messages 46 according to the present CAN FD format forassociated communication control device 11, 31 or receive the messagesfrom same, as needed.

A formation and then transfer of messages 45 having the CAN XL format,in addition to the reception of such messages 45, is achievable by useof the two user stations 10, 30.

FIG. 2 shows for message 45 a CAN XL frame 450, which is provided bycommunication control device 11 for transceiver device 12 fortransmitting onto bus 40. In the present exemplary embodiment,communication control device 11 creates frame 450 so as to be compatiblewith CAN FD, as also illustrated in FIG. 2. The same analogously appliesfor communication control device 31 and transceiver device 32 of userstation 30.

According to FIG. 2, for the CAN communication on bus 40, CAN XL frame450 is divided into different communication phases 451, 452, namely, anarbitration phase 451 and a data phase 452. Frame 450 includes anarbitration field 453, a control field 454, a data field 455, a checksum field 456 for a check sum FCRC, a switchover sequence ADS, and anacknowledgment field 457.

In arbitration phase 451, with the aid of an identifier ID inarbitration field 453, bit-by-bit negotiation is carried out betweenuser stations 10, 20, 30 concerning which user station 10, 20, 30 wouldlike to transmit message 45, 46 having the highest priority, andtherefore for the next time period for transmitting in subsequent dataphase 452 obtains exclusive access to bus 40 of bus system 1. A physicallayer, similarly as with CAN and CAN FD, is used in arbitration phase451. The physical layer corresponds to the bit transfer layer or layerone of the conventional Open Systems Interconnection (OSI) model.

An important point during phase 451 is that the conventional CSMA/CRmethod is used, which allows simultaneous access of user stations 10,20, 30 to bus 40 without destroying higher-priority message 45, 46. Itis thus possible to add further bus user stations 10, 20, 30 to bussystem 1 in a relatively simple manner, which is very advantageous.

Consequently, the CSMA/CR method must provide so-called recessive stateson bus 40, which may be overwritten by other user stations 10, 20, 30with dominant states on bus 40. In the recessive state, high-impedanceconditions prevail at individual user station 10, 20, 30, which incombination with the parasites of the bus wiring result in longer timeconstants. This results in a limitation of the maximum bit rate of thepresent-day CAN FD physical layer to approximately 2 megabits per secondat the present time during actual vehicle use.

In data phase 452, in addition to a portion of control field 454, theuseful data of the CAN XL frame or of message 45 from data field 455 andcheck sum field 456 for check sum FCRC, and also a field DAS, which isused to switch over from data phase 452 back to data phase 451, aretransmitted.

A sender of message 45 starts a transmission of bits of data phase 452onto bus 40 only after user station 10, as the sender, has won thearbitration, and user station 10, as the sender, thus has exclusiveaccess to bus 40 of bus system 1 for the transmission.

In general, in the bus system with CAN XL, in comparison to CAN or CANFD the following differing properties may be achieved:

-   a) acquiring and optionally adapting proven properties that are    responsible for the robustness and user-friendliness of CAN and CAN    FD, in particular a frame structure including identifiers and    arbitration according to the CSMA/CR method,-   b) increasing the net data transfer rate, in particular to    approximately 10 megabits per second,-   c) increasing the quantity of the useful data per frame, in    particular to approximately 4 kbytes or some other arbitrary value.

As illustrated in FIG. 2, in arbitration phase 451 user station 10partially uses as the first communication phase, in particular up to andincluding the FDF bit, a format from CAN/CAN FD according to ISO11898-1:2015. In contrast, beginning with the FDF bit in the firstcommunication phase and in the second communication phase (data phase452), user station 10 uses a CAN XL format, as described below.

In the present exemplary embodiment, CAN XL and CAN FD are compatible.The res bit from CAN FD, referred to below as the XLF bit, is utilizedfor switching from the CAN FD format over to the CAN XL format.Therefore, the frame formats of CAN FD and CAN XL are identical up tothe res bit. Not until the res bit does a receiver detect in whichformat the frame is transmitted. A CAN XL user station, i.e., userstations 10, 30 here, also support(s) CAN FD.

As an alternative to frame 450 shown in FIG. 2, in which an identifierincluding 11 bits is used, a CAN XL expanded frame format is optionallypossible in which an identifier including 29 bits is used. Up until theFDF bit, this is identical to the CAN FD expanded frame format from ISO11898-1:2015.

According to FIG. 2, frame 450 from the SOF bit up to and including theFDF bit is identical to the CAN FD base frame format according to ISO11898-1:2015. Therefore, the conventional structure is not furtherexplained here. Bits illustrated with a thick bar at their lower line inFIG. 2 are transmitted in frame 450 as dominant or “0.” Bits illustratedwith a thick bar at their upper line in FIG. 2 are transmitted in frame450 as recessive or “1.” In CAN XL data phase 452, symmetrical “1” and“0” levels are used instead of recessive and dominant levels.

In general, two different stuffing rules are applied in the generationof frame 450. Up until the XLF bit in control field 454, the dynamic bitstuffing rule from CAN FD applies, so that an inverse stuff bit is to beinserted after 5 identical bits in succession. A fixed stuffing ruleapplies after a resXL bit in control field 454, so that a fixed stuffbit is to be inserted after a fixed number of bits. Alternatively,instead of only one stuff bit, 2 or more bits may be inserted as fixedstuff bits, as also described in greater detail below.

In frame 450, the FDF bit is directly followed by the XLF bit, whichfrom the position corresponds to the “res bit” in the CAN FD base frameformat, as mentioned above. If the XLF bit is transmitted as 1, i.e.,recessive, it thus identifies frame 450 as a CAN XL frame. For a CAN FDframe, communication control device 11 sets the XLF bit as 0, i.e.,dominant.

In frame 450, the XLF bit is followed by a resXL bit, which is adominant bit for future use. For frame 450, the resXL [bit] must betransmitted as 0, i.e., dominant. However, if user station 10 receives aresXL bit as 1, i.e., recessive, receiving user station 10 goes into aprotocol exception state, for example, as carried out with a CAN FDmessage 46 for res=1. Alternatively, the resXL bit could be defined theopposite way, i.e., that it must be transmitted as 1, i.e., recessive.In this case, for a dominant resXL bit the receiving user station goesinto the protocol exception state.

In frame 450, the resXL bit is followed by a sequence ADS (arbitrationdata switch), in which a predetermined bit sequence is encoded. This bitsequence allows a simple and reliable switch from the bit rate ofarbitration phase 451 (arbitration bit rate) over to the bit rate ofdata phase 452 (data bit rate). For example, the bit sequence of the ADSsequence is made up of an AL1 bit that is transmitted as dominant, i.e.,0. The AL1 bit is the last bit of arbitration phase 451. The physicallayer in transceiver device 12, 22, 32 is switched over within the AL1bit. The two subsequent bits DH1 and DL1 are already transmitted at thedata bit rate. For CAN XL, bits DH1 and DL1 are thus temporally shortbits of data phase 452.

In frame 450, sequence ADS is followed by a PT field that denotes thecontents of data field 455. The contents indicate what type ofinformation is contained in data field 455. For example, the PT fieldindicates whether an Internet Protocol (IP) frame, a tunneled Ethernetframe, or some other frame is present in data field 455.

The PT field is followed by a DLC field into which data length code DLC,which indicates the number of bytes in data field 455 of frame 450, isinserted. Data length code DLC may assume any value from 0 up to themaximum length of data field 455 or the data field length. If themaximum data field length is in particular 2048 bits, data length codeDLC requires 11 bits, under the assumptions that DLC=0 means a datafield length that includes 1 byte, and DLC=2047 means a data fieldlength that includes 2048 bytes. Alternatively, data field 455 havingthe length 0 could be allowed, as with CAN, for example. DLC=0 wouldencode, for example, the data field length with 0 byte. With 11 bits,for example, the maximum encodable data field length is then(2{circumflex over ( )}11)−1=2047.

In frame 450, the DLC field is followed by a header check sum HCRC.Header check sum HCRC is a check sum for safeguarding the header offrame 450, i.e., all bits from the start of frame 450 including the SOFbit to the start of header check sum HCRC, including all dynamic, andoptionally, fixed, stuff bits up to the start of header check sum HCRC.The length of header check sum HCRC, and thus of the check sumpolynomial according to cyclic redundancy check CRC, is to be selectedcorresponding to the desired Hamming distance. For a data length codeDLC of 11 bits, the data word to be safeguarded by header check sum HCRCis longer than 27 bits. Therefore, in order to achieve a Hammingdistance of 6, the polynomial of header check sum HCRC must be at least13 bits long.

In frame 450, header check sum HCRC is followed by data field 455. Datafield 455 is made up of 1 to n data bytes, where n is, for example, 2048bytes or 4096 bytes or some other arbitrary value. Alternatively, a datafield length of 0 is possible. The length of data field 455 is encodedin the DLC field, as described above.

In frame 450, data field 455 is followed by a frame check sum FCRC.Frame check sum FCRC is made up of the bits of frame check sum FCRC. Thelength of frame check sum FCRC, and thus of the CRC polynomial, is to beselected corresponding to the desired Hamming distance. Frame check sumFCRC safeguards entire frame 450. Alternatively, only data field 455 isoptionally safeguarded with frame check sum FCRC.

In frame 450, frame check sum FCRC is followed by sequence DAS (dataarbitration switch) in which a predetermined bit sequence is encoded.This bit sequence allows a simple and reliable switch from the data bitrate of data phase 452 over to the arbitration bit rate of arbitrationphase 451. For example, the bit sequence of sequence DAS is made up of arecessive arbitration bit DH2 followed by a dominant arbitration bitDL2. In this example, the bit rate may be switched over at the edgebetween the two stated bits. The DAS field generally includes threebits, i.e., the DH2 bit, the DL2 bit, and an AH1 bit. Of the bits, thefirst bit and last bit are transmitted as recessive, i.e., 1, and themiddle bit is transmitted as dominant, i.e., 0.

In a departure from the preceding example, in the present exemplaryembodiment, sequence DAS contains a field FCP via which user stations10, 30, in particular their format check modules 15, 35, are able todetect in a received frame 450 a shift of the bit stream. The longer thebit pattern of the FCP field, the greater or stronger is the shift thatmay be detected in receiving user station 10, 30. The most advantageousbit pattern for the shift detection contains an even number of M bits,the first M/2 bits containing a 1 and the subsequent M/2 bits containinga 0. In the example from FIG. 2, with an FCP field including 4 bits, thefirst two bits are transmitted as recessive, i.e., 1. The last two bitsof the FCP field are transmitted as dominant, i.e., 0. Thus, the FCPfield including four bits according to FIG. 2, due to additional bitsDH3, DL3, differs from the customary two bits at the start of the DASfield. However, the edge from recessive to dominant in the FCP fieldfrom FIG. 2 may fulfill the same function as in a customary DAS field,which does not include bits DH3, DL3.

In general, it is possible that in the FCP field, the first M/2 bitscontain a 0 and the subsequent M/2 bits contain a 1. A shift by M−1 maybe detected using field FCP. This is described in greater detail belowwith reference to FIG. 3.

In frame 450, sequence DAS is followed by an acknowledgment field 457,which starts with an RP field. A synchronization pattern (sync pattern)is kept in the RP field, and allows a receiving user station 10, 30 todetect the start of arbitration phase 451 after data phase 452. Thesynchronization pattern allows receiving user station 10, 30, whichcannot detect the correct length of data field 455, for example due toan erroneous header check sum HCRC, to synchronize. These user stationsmay subsequently transmit a “negative acknowledge” in order tocommunicate the incorrect reception. This is very important inparticular when CAN XL no longer allows error frames 47 (error flags) indata field 455.

The RP field is followed by an acknowledgment (ACK) field 457 made up ofmultiple bits for acknowledgment or non-acknowledgment of a correctreceipt of frame 450. In the example of FIG. 2, an ACK bit, an ACK dlmbit, a NACK bit, and a NACK dlm bit are provided. The NACK bit and theNACK dlm bit are optional bits. Receiving user stations 10, 30 transmitthe ACK bit as dominant when they have correctly received frame 450. Thetransmitting user station transmits the ACK bit as recessive. Therefore,the bit in frame 450 originally transmitted onto bus 40 may beoverwritten by receiving user stations 10, 30. The ACK dlm bit istransmitted as a recessive bit, which is used for separation from otherfields. The NACK bit and the NACK dlm bit are used so that a receivinguser station may signal an incorrect reception of frame 450 on bus 40.The function of the bits is the same as that of the ACK bit and the ACKdlm bit.

In frame 450, acknowledgment (ACK) field 457 is followed by an end field(end of frame (EOF)). The bit sequence of end field EOF is used todenote the end of frame 450. End field EOF ensures that 8 recessive bitsare transmitted at the end of frame 450. This is a bit sequence thatcannot occur within frame 450. As a result, the end of frame 450 may bereliably detected by user stations 10, 20, 30.

End field EOF has a length that is different, depending on whether adominant bit or a recessive bit has been observed in the NACK bit. Ifthe transmitting user station has received the NACK bit as dominant, endfield EOF includes 7 recessive bits. Otherwise, end field EOF is only 5recessive bits long.

In frame 450, end field EOF is followed by an interframe space IFS, notillustrated in FIG. 2. This interframe space IFS is designed accordingto ISO 11898-1:2015, as with CAN FD.

FIG. 3 shows the basic design of user station 10 together withcommunication control device 11, transceiver device 12, and format checkmodule 15, which is part of communication control device 11. Userstation 30 has a design similar to that shown in FIG. 3, except thatformat check module 35 according to FIG. 1 is situated separately fromcommunication control device 31 and transceiver device 32. Therefore,user station 30 is not separately described.

According to FIG. 3, in addition to communication control device 11 andtransceiver device 12, user station 10 includes a microcontroller 13with which control device 11 is associated, and a systemapplication-specific integrated circuit (ASIC) 16, which alternativelymay be a system base chip (SBC) on which multiple functions necessaryfor an electronics assembly of user station 10 are combined. In additionto transceiver device 12, an energy supply device 17 that suppliestransceiver device 12 with electrical energy is installed in system ASIC16. Energy supply device 17 generally supplies a voltage CAN Supply of 5V. However, depending on the requirements, energy supply device 17 maysupply some other voltage having a different value. Additionally oralternatively, energy supply device 17 may be designed as a powersource.

Format check module 15 includes an insertion block 151 and an evaluationblock 152, which are described in greater detail below.

Transceiver device 12 also includes a transmission module 121 and areception module 122. Even though transceiver device 12 is consistentlyreferred to below, it is alternatively possible to provide receptionmodule 122 in a separate device externally from transmission module 121.Transmission module 121 and reception module 122 may be designed as aconventional transceiver device 22. Transmission module 121 may inparticular include at least one operational amplifier and/or onetransistor. Reception module 122 may in particular include at least oneoperational amplifier and/or one transistor.

Transceiver device 12 is connected to bus 40, or more precisely, to itsfirst bus wire 41 for CAN_H or CAN XL_H and its second bus wire 42 forCAN_L or CAN XL_L. The supplying of voltage for energy supply device 17for supplying first and second bus wires 41, 42 with electrical energy,in particular with voltage CAN Supply, takes place via at least oneterminal 43. The connection to ground or CAN_GND is achieved via aterminal 44. First and second bus wires 41, 42 are terminated via aterminating resistor 49.

In transceiver device 12, first and second bus wires 41, 42 are not justconnected to transmission module 121, also referred to as a transmitter,and to reception module 122, also referred to as a receiver, even thoughthe connection in FIG. 3 is not shown for simplification.

During operation of bus system 1, transmission module 121 converts atransmission signal TXD or TxD of communication control device 11 intocorresponding signals CAN XL_H and CAN XL_L for bus wires 41, 42, andtransmits these signals CAN XL_H and CAN XL_L onto bus 40 at theterminals for CAN_H and CAN_L.

According to FIG. 4, reception module 122 forms a reception signal RXDor RxD from signals CAN XL_H and CAN XL_L that are received from bus 40,and passes it on to communication control device 11, as shown in FIG. 3.With the exception of an idle or standby state, transceiver device 12with reception module 122 during normal operation always listens to atransfer of data or messages 45, 46 on bus 40, in particular regardlessof whether or not transceiver device 12 is the sender of message 45.

According to the example from FIG. 4, signals CAN XL_H and CAN XL_L, atleast in arbitration phase 451, include dominant and recessive buslevels 401, 402, as from CAN. A difference signal VDIFF=CAN XL_H−CANXL_L, shown in FIG. 5, is formed on bus 40. The individual bits ofsignal VDIFF with bit time t_bt may be detected using a receptionthreshold of 0.7 V. In data phase 452 the bits of signals CAN XL_H andCAN XL_L are transmitted more quickly, i.e., with a shorter bit timet_bt, than in arbitration phase 451. Thus, signals CAN XL_H and CAN XL_Lin data phase 452 differ from conventional signals CAN_H and CAN_L, atleast in their faster bit rate.

The sequence of states 401, 402 for signals CAN XL_H, CAN XL_L in FIG. 4and the resulting pattern of voltage VDIFF from FIG. 5 are used only forillustrating the function of user station 10. The sequence of datastates for bus states 401, 402 is selectable as needed.

In other words, transmitter 121 in a first operating mode according toFIG. 4 generates a first data state as bus state 402 with different buslevels for two bus wires 41, 42 of the bus line, and a second data stateas bus state 401 with the same bus level for the two bus wires 41, 42 ofthe bus line of bus 40.

In addition, transmitter 121 transmits the bits onto bus 40 at a higherbit rate for the temporal profiles of signals CAN XL_H, CAN XL_L in asecond operating mode, which includes data phase 452. CAN XL_H and CANXL_L signals may also be generated in data phase 452 with a differentphysical layer than with CAN FD. The bit rate in data phase 452 may thusbe increased even further than with CAN FD.

Format check module 15 from FIG. 3, in particular its insertion block151, is used to insert the FCP field into frame 450 when user station 10acts as the sender of frame 450. In the example from FIG. 2, insertionblock 151 has inserted only a single FCP field into frame 450. The FCPfield is placed in frame 450 as late as possible so that shifts at theend of frame 450 are also detectable. A placement after frame check sumFCRC, as shown in FIG. 2 as an example, is very advantageous since thisis the last possible position.

In the present exemplary embodiment, format check module 15 from FIG. 3is designed in such a way that the FCP field replaces the DH2 bits andthe DL2 bits of the DAS field. For this purpose, the FCP field must beselected as 1100 or 111000, etc., so that the function of DH2/DL2 isretained. Thus, the FCP field is used not only to enable a reliableformat check, but also as a synchronization edge prior to the switchoverfrom data phase 452 into arbitration phase 451. The FCP field thus hastwo different functions. As a result, the FCP field generates as littledata overhead as possible.

Format check module 15 from FIG. 3 is optionally designed toalternatively or additionally integrate the FCP field into the ADSfield. Insertion block 151 may thus insert at least one FCP field intoframe 450.

Evaluation block 152 of format check module 15 from FIG. 3 is used tocheck the format of the bit stream received from bus 40, using the FCPfield.

If the FCP field includes M=4 bits, for example, insertion block 151 mayinsert the FCP field as “1100” or “0011.” Consequently, the FCP field istransmitted as “1100” or “0011.” If receiving user station 10 samplessome other value for the FCP field, using evaluation block 152,evaluation block 152 evaluates this to mean that a shift of the bitstream of frame 450 is present. With such a bit sequence in the FCPfield, receiving user station 10 may reliably detect, using evaluationblock 152, a shift of the bit stream received from bus 40 by M−1=3 bitsto the left or by M−1=3 bits to the right. This is illustrated in thefollowing table.

Sampling result for Case receiving user station Shift to the right by 3bits    0xxx Shift to the right by 2 bits   00xx Shift to the right by 1bit  100x No shift 1100 Shift to the left by 1 bit x110  Shift to theleft by 2 bits xx11   Shift to the left by 3 bits xxx1   

In the table, x stands for an arbitrary bit value, i.e., 0 or 1. The FCPfield is transmitted as “1100,” as indicated in the middle of the table.If no edge shift, and thus no shift of the bit stream, takes place, thereceiving user station also samples the FCP field as “1100.”

Above and below the transmitted field “1100,” the table illustrates thecases in which receiving user station 10 (reception node), which in thisexample is not a sender of frame 450, samples the bit stream in ashifted manner due to an error. “Shift to the right by 3 bits” meansthat the view of the receiving user station (reception node) is shiftedby 3 bits, and in particular in this case is late by 3 bits.Accordingly, receiving user station 10 (reception node) samples the lastbit of the transmitted FCP field as the first bit of the received FCPfield. The other three bits of the received FCP field then havedifferent values, denoted here by “x.”

“Shift to the left by 1 bit” means that the view of receiving userstation 10 (reception node) is shifted by 1 bit, and in particular inthis case is early by 1 bit. Accordingly, receiving user station 10(reception node) samples the first 3 bits of the transmitted FCP fieldas the last bit of the received FCP field.

It is apparent from the table that the value of the FCP field sampled byreceiving user station 10 (reception node), independently of the valuethat the bits denoted by “x” have, for a shift is always different, inat least one bit, from the expected value of the FCP field. Receivinguser station 10 (reception node), in particular its format check module15 and more precisely its evaluation block 152, may thus detect theshift, i.e., the error, in the received bit stream. Evaluation block 152outputs a corresponding communication to communication control device11. Received frame 450 may thus be discarded in the event of an error.As a result, communication control device 11 may transmit an error frame47 to bus 40.

According to another example of a fixed value of the FCP field in thepresent exemplary embodiment, the FCP field includes 6 bits, so that M=6bits. Insertion block 151 thus inserts the FCP field as “111000” or“000111.” Consequently, the FCP field is transmitted as “111000” or“000111.” If receiving user station 10, which is not a sender of theframe, samples some other value for the FCP field, using evaluationblock 152, evaluation block 152 evaluates this to mean that a shift ofthe bit stream is present. With such a bit sequence in the FCP field,receiving user station 10 may reliably detect, using evaluation block152, a shift of the bit stream received from bus 40 by M−1=5 bits to theleft or to the right.

Of course, other fixed lengths of the FCP field, and thus other fixedvalues of the FCP field, are possible.

According to one modification of the present exemplary embodiment, theFCP field has variable contents.

As an example of such variable contents of the FCP field, the number offixed stuff bits in the FCP field may be transferred. The number offixed stuff bits is a function of the length of frame 450. If the widthof the FCP field, i.e., the number of bits that are provided in frame450 for the FCP field, is not adequate to transfer the entire number offixed stuff bits, only the less significant bits of a fixed stuff bitcounter may be transmitted.

As another example of such variable contents of the FCP field, thenumber of frames 450 in the FCP field transmitted by a transmitting userstation (transmission node) may be transferred. The number of frames 450transmitted by a transmission node may also be referred to as a framecounter.

FIG. 6 shows a frame 450_1 according to a second exemplary embodiment inwhich CAN XL and CAN FD are compatible. In this exemplary embodiment,frame 450_1 and thus the CAN XL frame format are different from frame450 from FIG. 2, as described below. Only the differences from frame 450from FIG. 2 are described below. In other respects, frames 450, 450_1 ofthe two exemplary embodiments are the same.

At least two FCP fields are present in frame 450_1. In the example fromFIG. 6, in frame 450_1, an FCP field FCP1 is inserted after header checksum HCRC, and an FCP field FCP2 is inserted after frame check sum FCRC.Also for frame 450_1, FCP fields FCP1, FCP2 have a length M=4 bits as anexample. Of course, some other length for the FCP field may be selected.In particular, it is possible for the lengths, i.e., the number of bitsof FCP fields FCP1, FCP2, to be different.

In general, insertion block 151 may be designed to insert an FCP fieldat an arbitrary position in frame 450_1. Evaluation block 152 isdesigned to search the FCP field at the insertion points in question andthus evaluate received frame 450_1.

In particular, insertion block 151 is designed to insert an FCP fieldmultiple times into frame 450_1 to be transmitted. For example, an FCPfield may always be inserted with the same contents, always after apredetermined number of pieces of data, in particular always after 128bytes of data or some other arbitrary value. Of course, other examplesare possible.

FIG. 7 shows a frame 4500 according to a third exemplary embodiment inwhich the frame formats of CAN XL and CAN FD are not compatible. In thisexemplary embodiment, frame 4500 and thus the CAN XL frame format aredifferent from frame 450 from FIG. 2, as described below. Only thedifferences from frame 450 from FIG. 2 are described. In other respects,frames 450, 4500 of the two exemplary embodiments are the same.

In general, when creating frame 4500 according to the present exemplaryembodiment only the fixed stuffing rule is used, so that a fixed stuffbit is to be inserted after a fixed number of bits. Alternatively,instead of only one stuff bit, two or more bits may also be inserted asfixed stuff bits. For a known value of data length code DLC, thisresults in a constant frame length or a constant length of frame 4500.This prevents various problems that are caused by dynamic stuff bits.

In frame 4500 according to the present exemplary embodiment, identifierID is no longer limited to 11 bits or 29 bits as with CAN FD. Number kof the bits of identifier ID may be freely selected. However, number kis alternatively settable to a fixed value. For a high net data rate, anID including k=8 bits is reasonable. This is sufficient to give eachuser station 10, 20, 30 of bus system 1 an adequate number of bus accesspriorities. Of course, some other value of k is selectable, depending onthe need and the number of various priorities in bus system 1.

Bits RRS, IDE, FDF, XLF of frame 450 from FIG. 2 are no longer necessaryin frame 4500 and are omitted. This saves 4 bits, so that the frameoverhead is reduced. The net data rate in bus system 1 is thusincreased.

End field EOF includes only 5 bits in frame 4500 when the NACK bit isdominant. In contrast, if the NACK bit is recessive, end field EOFincludes 3 bits. This ensures that 6 recessive bits are transmitted atthe end of frame 4500. This number of recessive bits cannot occur at anyother location in a valid frame 4500 when a fixed stuff bit is insertedafter 5 identical bits in arbitration phase 451. Alternatively, therecould be more than 6 bits. In particular, the number of EOF bits must beadapted to the number of bits after which a fixed stuff bit is inserted.

Interframe space IFS does not require a minimum length in frame 4500. Inparticular, interframe space IFS may have the length 0. In such a case,two frames 4500 are seamlessly transmitted in succession. However, aninterframe space IFS that includes 1 bit, for example, is alsoreasonable in order to increase the robustness of bus system 1 incomparison to the previously stated case. Due to the now 7 recessivebits between two frames 4500, a new user station at bus 40 maysynchronize more reliably.

According to a fourth exemplary embodiment, the FCP field is used as afixed stuff bit. In other words, insertion block 151 is designed toinsert an FCP field instead of a fixed stuff bit into frame 450. In sucha case, a short FCP field, for example having the length M=2 bits, issufficient, since only a small shift may result between two stuff bits.

Thus, also in the present exemplary embodiment, the FCP field has twodifferent functions, namely, stuff bit and format check.

An FCP field having a length M=2 bits results in a very low dataoverhead, or even no data overhead at all. This is explained in greaterdetail below.

In the present exemplary embodiment, an FCP field with constant contentsis always used instead of a fixed stuff bit. The bit pattern in the FCPfield is selected by insertion block 151 in such a way that the FCPfield contains a synchronization edge. If CAN XL synchronizes to fallingedges, the value “10” would be advantageous for the FCP field. If CAN XLwere synchronized to the rising edge, the value “01” would beadvantageous for the FCP field.

For fixed stuff bits, in the worst case for the synchronization afalling edge is present only after every other stuff bit.

Since synchronization may always be carried out for an FCP field, thedistance between two FCP fields may thus be twice as great as thedistance between two fixed stuff bits without adversely affecting thesynchronization of a receiving user station 10, 30 (reception node).

Since the FCP field includes 2 bits, but occurs only half as often as afixed stuff bit, the data overhead due to the FCP field is identical tothe data overhead that is generated by fixed stuff bits.

The great advantage of the FCP field is that its contents are constant.It is thus possible to reliably determine shifts in the data stream. Inthe described example with M=2 bits, shifts in receiving user station10, 30 (reception node) by 1 bit may be reliably detected. As a resultof the FPC [sic; FCP] field occurring so often in the frame, shifts maybe detected immediately and effectively. An error in received frame 450may thus be detected very quickly, and the transmission of frame 450 maybe quickly aborted. This contributes to a faster transfer of useful datain bus system 1.

According to one modification of the present exemplary embodiment,receiving user station 10, 30 (CAN XL reception node) may carry out aresynchronization only at the edges in the FCP field instead ofresynchronizing at each falling edge. Due to the resynchronization thusbeing limited to the necessary edges, the risk of receiving user station10, 30 (CAN XL reception node) synchronizing to a faulty edge, and thusinserting an error, is reduced.

The great advantage of this modification of the present exemplaryembodiment is that the number of resynchronization errors decreases,since the edges in the FCP field must now be explicitly faulty in orderfor a mis-synchronization to take place.

According to a fifth exemplary embodiment, the FCP field is once againused as a fixed stuff bit, as in the preceding exemplary embodiment.However, in the present exemplary embodiment an FCP field with variablecontents is always used instead of a fixed stuff bit. Thus, also in thepresent exemplary embodiment, the FCP field has two different functions,namely, stuff bit and format check.

Insertion block 151 always selects an FCP field that is appropriate forthe value of the stuff bit. Since a stuff bit may have two values,namely, 0 or 1, two different FCP fields are used. Thus, insertion block151 may either insert an FCP field FCP_A having the value “01,” or anFCP field FCP B having the value “10.”

Therefore, insertion block 151 inserts an FCP field depending on thevalue of the potential stuff bit. For example, FCP field FCP_A would beinserted and transmitted when the stuff bit is 0. If the stuff bit is 1,FCP field FCP B would be inserted and transmitted.

Of course, for insertion block 151 the principle of the variablecontents of the FCP field is applicable to the generation of other FCPfields.

According to a sixth exemplary embodiment, the AH1 bit is used as anadditional or single FCP field. This is possible when the AH1 bit is notevaluated in some other way according to the present standardizedversion of CAN XL. At the present time, the AH1 bit is used solely tohave time in transceiver device 12, 32 for a switchover of the physicallayer from data phase 452 into arbitration phase 451.

In such a case, the reception node may signal to transceiver device 12,32 the switchover of the physical layer, for example via a TXD line.This is possible due to the fact that the reception node does not useits TXD line for transmission. This does not occur in the transmissionnode, since the transmission node uses its TXD line for transmission.

As a result, the reception node or user station 10 as a receiving userstation may evaluate, i.e., sample, the AH1 bit, using its evaluationblock 152. Since the AH1 bit has a constant value, it is also used tocheck the format of the received frame (format check). The AH1 bitassists in detecting whether the reception node samples the bit streamin a shifted manner. The check of the format of the received frame(format check) may thus be reliably carried out, or further reinforcedfor additional FCP fields.

The evaluation of the AH1 bit has the advantage that the check of theformat (format check) of received frame 450 does not result in dataoverhead. Thus, also in the present exemplary embodiment, the FCP fieldhas two different functions, namely, the function of the previous AH1bit and format check.

All of the above-described embodiments of user stations 10, 20, 30, ofbus system 1, and of the method carried out therein may be used alone orin any possible combination. In particular, all features of theabove-described exemplary embodiments and/or modifications thereof maybe arbitrarily combined. Additionally or alternatively, in particularthe following modifications are possible.

Although the present invention is described above with the example ofthe CAN bus system, the present invention may be employed for anycommunications network and/or communication method in which twodifferent communication phases are used in which the bus states, whichare generated for the different communication phases, differ. Inparticular, the present invention is usable for developments of otherserial communications networks, such as Ethernet and/or 100Base-T1Ethernet, field bus systems, etc.

In particular, bus system 1 according to the exemplary embodiments mayalso be a communications network in which data are serially transferableat two different bit rates. It is advantageous, but not a mandatoryrequirement, that in bus system 1, exclusive, collision-free access of auser station 10, 20, 30 to a shared channel is ensured, at least forcertain time periods.

The number and arrangement of user stations 10, 20, 30 in bus system 1of the exemplary embodiments is arbitrary. In particular, user station20 in bus system 1 may be dispensed with. It is possible for one ormultiple of user stations 10 or 30 to be present in bus system 1. It ispossible for all user stations in bus system 1 to have the same design,i.e., for only user station 10 or only user station 30 to be present.

1-15. (canceled)
 16. A user station for a serial bus system, comprising:a communication control device configured to control a communication ofthe user station with at least one other user station of the bus system;and a transceiver device configured to transmit a transmission signal,generated by the communication control device, onto a bus of the bussystem, so that for a message that is exchanged between the userstations of the bus system, a bit time of a signal transmitted onto thebus in a first communication phase may differ from a bit time of asignal transmitted in a second communication phase; wherein thecommunication control device is configured to generate the transmissionsignal according to a frame, and to insert into the frame at least onefield that is configured for checking whether a bit stream of the framein a user station of the bus system that receives the frame is shiftedby at least one bit compared to an expected frame.
 17. The user stationas recited in claim 16, wherein the communication control device isconfigured to insert the at least one field into the frame after a datafield.
 18. The user station as recited in claim 16, wherein thecommunication control device is configured to insert the at least onefield into the frame after a frame check sum that has been formed overall bits in the frame.
 19. The user station as recited in claim 16,wherein the communication control device configured to insert the atleast one field prior to a data field in which useful data of the frameare inserted.
 20. The user station as recited in claim 16, wherein thecommunication control device is configured to configure and/or arrangethe at least one field in such a way that contents of the at least onefield in a receiving user station are to be used not only for a functionof checking the shift of the bit stream, but also for a differentfunction.
 21. The user station as recited in claim 16, wherein thecommunication control device is configured to always insert one of theat least one fields into the frame after a fixed number of bits.
 22. Theuser station as recited in claim 16, wherein the communication controldevice is configured to insert the at least one field into the frame asa fixed stuff bit, and the communication control device is configured toinsert all fixed stuff bits into the frame according to a fixed bitstuffing rule, according to which a fixed stuff bit is to be insertedafter a fixed number of bits.
 23. The user station as recited in claim22, wherein the communication control device is configured to select avalue of the at least one field as a function of which value would beselected for the stuff bit in order to insert an inverse stuff bit intothe frame after five identical bits in succession.
 24. The user stationas recited in claim 16, wherein the communication control device isconfigured to use the same value for all of the at least one field inthe frame.
 25. The user station as recited in claim 24, wherein thecommunication control device is configured to use an even number of Mbits for the at least one field, a first half of the M bits in each casehaving the same first value, and the second half of the M bits in eachcase having the same second value, which is inverse to the first value.26. The user station as recited in claim 24, wherein the communicationcontrol device is configured to insert into the at least one field atleast the least significant bits of a number of fixed stuff bits thatare inserted into the frame.
 27. The user station as recited in claim24, wherein the communication control device is configured to insertinto the at least one field at least the least significant bits of anumber of frames that have been already been transmitted onto the busfrom the communication control device.
 28. The user station as recitedin claim 16, wherein the communication control device is configured toprovide a bit after a switchover of the second communication phase intothe first communication phase, during which the transceiver device hastime to switch over into the second communication phase, and thecommunication control device is configured to, in the case in which theuser station of the bus system receives the frame but is not a sender ofthe frame, to use the bit to check whether the bit stream of thereceived frame is shifted by at least one bit compared to the expectedframe.
 29. The user station as recited in claim 16, wherein the framethat is formed for the message has a configuration that is compatiblewith CAN FD, and in the first communication phase, it is negotiatedwhich of the user stations of the bus system in a subsequent secondcommunication phase obtains, at least temporarily, exclusive,collision-free access to the bus.
 30. A bus system, comprising: a bus;and at least two user stations that are connected to one another via thebus in such a way that they may communicate serially with one another,and of which at least one user station is a user station including: acommunication control device configured to control a communication ofthe user station with at least one other user station of the bus system,and a transceiver device configured to transmit a transmission signal,generated by the communication control device, onto a bus of the bussystem, so that for a message that is exchanged between the userstations of the bus system, a bit time of a signal transmitted onto thebus in a first communication phase may differ from a bit time of asignal transmitted in a second communication phase, wherein thecommunication control device is configured to generate the transmissionsignal according to a frame, and to insert into the frame at least onefield that is configured for checking whether a bit stream of the framein a user station of the bus system that receives the frame is shiftedby at least one bit compared to an expected frame.
 31. A method forcommunicating in a serial bus system, the method being carried out usinga user station of the bus system that includes a communication controldevice and a transceiver device, the method comprising the followingsteps: controlling, via the communication control device, acommunication of the user station with at least one other user stationof the bus system; and transmitting, via the transceiver device, atransmission signal, generated by the communication control device, ontoa bus of the bus system, so that for a message that is exchanged betweenuser stations of the bus system, a bit time of a signal that istransmitted onto the bus in a first communication phase may differ froma bit time of a signal that is transmitted in a second communicationphase, the communication control device generating the transmissionsignal according to a frame, and inserting into the frame at least onefield that is configured for checking whether a bit stream of the framein a user station of the bus system that receives the frame is shiftedby at least one bit compared to an expected frame.